Bores such as pipes or cylindrically shaped equipment are often constructed from welded segments that are subject to stress or wear. As such, there is often a need to inspect the interior surface of the bore during maintenance procedures for cracks and the integrity of a weld joint. For example, a reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has submerged bores that have interior welds that need to be inspected during maintenance routines. Hollow tubular jet pumps having internal bores are positioned within an annulus to provide the required reactor core water flow. The jet pumps include an upper portion known as the inlet mixer and a lower portion, known as the diffuser. The inlet mixer and the diffuser, due to their large size, are formed by welding a plurality of cylindrical and conical sections together. Specifically, respective ends of adjacent cylindrical sections are joined with a circumferential weld. During operation of the reactor, the circumferential weld joints may experience inter-granular stress corrosion cracking (IGSCC) and irradiation assisted stress corrosion cracking (IASCC) in weld heat affected zones which can diminish the structural integrity of the jet pump.
It is important to examine the welds of the jet pump inlet mixer and diffuser periodically to determine whether any cracking has occurred. While examinations in the annulus or region between a shroud and a pressure vessel wall can be performed, these examinations are likely to be only partial inspections due to access limitations in the annular region of the reactor. As such, the examination of the jet pump welds are often examined by an inspection tool positioned inside of the jet pump inlet mixer and jet pump diffuser. Such inspection tool performs ultrasonic and/or eddy current examinations of jet pump welds from inside the jet pump inlet mixer and diffuser in a nuclear reactor.
Typically, operational personnel located on a refuel bridge above the surface of the pool manipulate a tool delivery system that is connected to a jet pump inlet for insertion of an inspection probe. The long cylindrical inspection probe is inserted through the narrow opening of the jet pump inlet and is attached and vertically positioned within the jet pump by a guide cable. Once inside, the inspection probe is activated such that arms containing sensors are extended from the long cylindrical body of the inspection probe. The inspection probe sensing arms are rotated by a motor on the inspection probe to provide for a radial scan of the interior surfaces of the jet pump. The inspection probe often includes a stabilizing weight in an effort to stabilize the probe in the bore.